[Bundles] Log entry size and search index stats

[apurvabhaleMS]

Description

Adds bundle size, per-entry size, and per-entry search index statistics to the existing bundleStatistics log. This data is needed to choose safe defaults for upcoming bundle limits (bundle size, resource size, and search index values per resource) before any limit is enforced. This PR only adds logging; request behavior does not change.

New fields in bundleStatistics:

"totalBundleBytes": 24117248,
"entrySize": {
  "over5MiB": 2, "over10MiB": 1, "over20MiB": 0,
  "large": [ { "index": 3, "resourceType": "DocumentReference", "bytes": 11534336 } ]
},
"searchIndex": {
  "over100": 1, "over250": 1, "over500": 0,
  "heavy": [ { "index": 12, "resourceType": "Observation", "indexValues": 1450 } ]
}

Field	Meaning
totalBundleBytes	Request Content-Length; falls back to the sum of serialized entries when absent (chunked requests)
entrySize.overXMiB	Number of entries whose request body is larger than X MiB
entrySize.large	Top 5 entries larger than 5 MiB, largest first
searchIndex.overN	Number of entries whose resource produced more than N search index values
searchIndex.heavy	Top 5 entries with more than 100 search index values, highest first

How the data is collected:

• Entry size: BundleHandler.GenerateRequest already serializes each entry to bytes; the length is stored on ResourceExecutionContext. Sizes are registered for all entries when statistics are created, so they are logged even if the bundle fails partway.
• Search index values: ResourceWrapperFactory.Create stores searchIndices.Count on the request context only when ExecutingBatchOrTransaction is true. The sequential and parallel bundle paths read it from the entry's request context after the entry executes.
• No additional serialization, SQL calls, or log lines are introduced.

Related issues

Addresses AB#195352.

Testing

• New unit tests:
  • BundleHandlerStatisticsTests: buckets, top-5 ordering and cap, totalBundleBytes, and empty summaries.
  • ResourceWrapperFactoryTests: count stored for bundle entries; not stored outside a bundle.
  • BundleHandlerTests: end-to-end statistics for sequential and parallel batches; totalBundleBytes uses Content-Length when present.
• R4 API unit tests (BundleHandlerTests, BundleHandlerStatisticsTests): 44 passed. R4 Core unit tests (ResourceWrapperFactoryTests): 7 passed. R4 and STU3 build without warnings.

FHIR Team Checklist

• Update the title of the PR to be succinct and less than 65 characters
• Add a milestone to the PR for the sprint that it is merged (i.e. add S47)
• Tag the PR with the type of update: Bug, Build, Dependencies, Enhancement, New-Feature or Documentation
• Tag the PR with Open source, Azure API for FHIR (CosmosDB or common code) or Azure Healthcare APIs (SQL or common code) to specify where this change is intended to be released.
• Tag the PR with Schema Version backward compatible or Schema Version backward incompatible or Schema Version unchanged if this adds or updates Sql script which is/is not backward compatible with the code.
• When changing or adding behavior, if your code modifies the system design or changes design assumptions, please create and include an ADR.
• CI is green before merge
• Review squash-merge requirements

Semver Change (docs)

Patch

[Copilot]

🟡 Changes recommended

PATCH search-index telemetry attributes counts to payload types rather than the indexed target resource types.

1 open finding

• Use route resource type for PATCH indexing telemetry · New

What changed in this PR

Extends existing bundle telemetry to inform future limits without enforcing new request restrictions.

Changes:

• Logs total bundle bytes and per-entry size summaries.
• Captures search-index counts in sequential and parallel execution.
• Adds tests for collection, thresholds, and top-five summaries.

File	Description
src/​Microsoft.Health.Fhir.Shared.Core.UnitTests/​Features/​Persistence/​ResourceWrapperFactoryTests.cs	Tests bundle-only index-count capture.
src/​Microsoft.Health.Fhir.Shared.Api/​Features/​Resources/​Bundle/​BundleHandlerStatistics.cs	Adds size and index-count summaries.
src/​Microsoft.Health.Fhir.Shared.Api/​Features/​Resources/​Bundle/​BundleHandlerParallelOperations.cs	Collects parallel-entry statistics.
src/​Microsoft.Health.Fhir.Shared.Api/​Features/​Resources/​Bundle/​BundleHandler.cs	Records entry sizes, bundle totals, and index counts.
src/​Microsoft.Health.Fhir.Shared.Api.UnitTests/​Features/​Resources/​Bundle/​BundleHandlerTests.cs	Tests collection paths and Content-Length handling.
src/​Microsoft.Health.Fhir.Shared.Api.UnitTests/​Features/​Resources/​Bundle/​BundleHandlerStatisticsTests.cs	Tests buckets, ordering, caps, and empty summaries.
src/​Microsoft.Health.Fhir.Core/​Features/​Persistence/​ResourceWrapperFactory.cs	Stores index counts on bundle-entry request contexts.

🧠 Review effort: Balanced

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